In general, a construction machine such as a hydraulic excavator has a number of sliding bearings that are used under conditions including high contact pressure and slow speed sliding. For example, as shown in FIG. 5, a conventional hydraulic excavator 200 is configured to have an arm 210, with a bucket 220 being rotatably connected to a distal end of the arm 210. The arm and bucket are driven by a plurality of hydraulic cylinders 230 respectively. Coupling portions between the arm 210 and bucket 220 as well as ends of the hydraulic cylinders 230 are rotatably supported by sliding bearings 300 respectively.
During excavation, the sliding bearings 300 used at the above-described positions are subjected to extremely large contact pressure at sliding surfaces between bushes and shaft parts in the sliding bearings 300, and the bushes and shaft parts slide with respect to each other at a slow speed. Thus, the contact surfaces (sliding surfaces) between the bushes and shaft parts encounter severe lubrication conditions, and therefore seizure, scratching, uneven wear and other problems are likely to occur due to shortage of lubrication.
To avoid these problems, the prior art proposes, as disclosed in the below-mentioned Patent Documents 1 and 2, a porous sintered alloy bush that is used as a bush in sliding contact with the shaft part and that includes Fe and Cu as its major components. The sintered alloy bush is impregnated with high viscosity lubrication oil beforehand, so that the impregnated lubrication oil seeps onto the sliding surface under pressure and friction heat during sliding. This prevents the shortage of the lubrication oil at the sliding surface and related problems.